I am the legal caregiver of a very dear friend. We live in an RV Park. Can I be prevented from visiting her, even during this virus?

Mizbee, what type of visit are you seeking? There are still many unknowns about the coronavirus, so you are putting your friend at risk if you do not respect the social distancing recommendations. Also, I think it depends on what state you are in. Some states' restrictions are more enforced than others. When you say you are her legal caregiver, do you mean her durable PoA? If so, I would not have the office manager store that document. You should have it in your possession and store it yourself. Are you her legal guardian? Ditto to storing the paperwork. If you are neither of these things, then you have less of an excuse except that you miss her and are concerned for her. You can have a visit through a door or window like many others are doing at nursing homes. Everyone is making concessions to keep as many people healthy and protected as possible. It won't be forever.

You are doing the same care you would if you were employed by an agency hired to provide a caregiver. This is not a social call but a job.
If you glove and mask prior to entering her home and you follow the same protocol any other caregiver would follow I do not see how you can be restricted.
Is any other resident of the Park getting care from a hired Caregiver? Is anyone getting visits from a Hospice Nurse, CNA or therapist? If the answer to these is yes then they should not be able to restrict you from your job.
And to make it more reasonable you use one mask in this persons residence you change the mask when you leave and put on another mask. When you return to your residence you remove your mask and wash both (unless you are using single use ones in that case throw them out)

To answer the last part of your question..You are her caregiver, you should be going to her to provide care that is required she should not be coming to you. If she is able to come to you to "visit" this is then a social call and would then by definition be restricted according to your Managements restrictions.
On the other hand if your visits to her do not constitute "caregiving" then that also is a social call and would then be restricted.
If you had a schedule previously, example you would go to her place Monday, Wednesday, Friday to do what was necessary then you keep the same schedule or you cut back on it you do not increase the visits.

If you are her caregiver, no they can not stop you from doing your job.

You are living in a fish bowl being in an RV park, everyone sees your comings and goings, not an easy situation to be in.

I would document the entire situation, just in case you need it for future.

I am afraid that people don't understand that care needs can increase in situations and that requires more help not less.

Just be sure and wear a mask and gloves while you are in her home. I would put a stop to her coming to your home, that is probably the button being pushed. I carry a small spray bottle of rubbing alcohol and I spray everything before I touch it, I also spray my gloves frequently, then I can use the same pair for hours without fear of cross contamination. I even wash them as they were my bare skin. I use a N95 mask and cover that with a washable mask, that way I can spray alcohol on the N95 at the end of use and wash the one exposed to the air, thereby getting many uses out of the mask that is the real barrier. I tell you all this for ideas to use to protect yourself and your client without having to use items in excess that are not available.

Best of luck, I full timed RV'd for 6 years so I know what you are facing with a bunch of people stuck in their rigs. Oy vey!

Mizbee, who is trying to prevent you from offering care?

I know members of this forum live all over the world and within countries there are differing public health orders around Covid. There are many situations where logistically it is necessary to 'break' the rules in order to provide care for others.

My next door neighbour's son is still working, their daughter in law is a health care provider. Schools and day cares are closed, so they are looking after their 6 year old grandson each day.

I look after my grandson every weekend. Who else is going to provide care?

Let the words of the busy bodies roll over you and continue to provide the care needed for your friend.

It would be best if you go to her instead of the two of you going to each other's homes. That way if she is isolated, you can take precautions after going shopping etc, to prevent the spread to her home.