My mother makes me feel so guilty

You have nothing to feel guilty about as you are a wonderful daughter. However, you need to take care of yourself and do things you enjoy. Rather than visit 5 times a week, start by cutting back to 4 times a week and on your new "free" day do something for yourself. Your target is to visit only 3 days a week as this will be good for you as you will have more time for yourself and also give time for your Mother to adjust to her new home.

Are you feeling guilty because you cannot bring her back to your home to live with you, or because your siblings do not visit?

I'd tell mom, that it's because you love her that she's where she's at now. That she is getting the best possible care that you could no longer give her. Tell her you wish you could turn back the clock to when she was healthy and young and didn't need help, but you can't. Tell her you hear what she's saying and that you're not discounting it, but you're trying to be a good daughter and do what's right. And in YOUR opinion, it's the right thing to do. As far as your other siblings, unless they live in another state, take her to see them on one of the days you take her out. Make them visit with her, since they're obviously too preoccupied to do so on their own. If she were my mom and physically able, I'd be making her the traveling mother of all times. Traveling from one sibling to another.

My mother was in the same situation as you...she was the youngest of 9 and, of course, everyone assumed that Mom would be the one to take care of her mother, which she did. The sisters were involved but the brothers just sent birthday gifts, etc. You would think it was a national holiday whenever they got around to showing up!
Do not feel guilty about backing off a bit. If your mother is in good hands and all her needs are being met, then you have done the best thing for her. You cannot be responsible for anyone's happiness but your own. If you continue to "fix" everything for your Mom, including trying to make her happy, you will be dragged down with the undertoe...she will never stand on her own two feet, start meeting people at the facility, or participate in her own happiness.
I decided long ago that I had to divide myself into two people: 1) the daughter who can get emotional and feel bad about my Mom's decline...the one who listens to her concerns, etc., and 2) the person who is entrusted with her care and needs to make very logical and practical decisions about her living environment.
I would make one more plea to the sibs. Everyone can take 2 days out of the month to see her or call her or send her something. Get very specific..."Mom would really like to see you a couple times a month, it's been awhile since your last visit." or "Could you please send a little note to Mom or flowers or candy?" After that, it is their own sin if they do not care and I would go no further in trying to drag them there. (Also, doesn't she have a lot of grandchildren who are old enough to visit??)
Take care of yourself. Start planning what you want to do with your own life, and take time out of the day to think about anything but caregiving.
good luck....we're all in the same boat here!

Do you need a friend? You and I are very very similar. Believe me, I am in your same shoes. Maybe I can help you cope with it by sharing my experiences and visa versa.