How to get my 90 yr old mother to take meds when she can't?

A little more info please.
Are you asking how you can get her to take medications when she refuses?
Or are you asking how to get her to take them if she can not swallow or take pills?

Some medications can be crushed (Not capsules or time release) and put in pudding, stirred into ice cream or mixed with a bit of applesauce.
Most medications can be ordered in liquid form so it is easier for a person that can not take pills. If the person can not swallow liquids the liquid medication can be mixed with a thickener or again mixed into pudding or applesauce.
If she is of sound mind she can refuse medications it is her right.

Sorry, she can't what? Please come back to add more.

Another tip for swallowing is to sit up and lean forward slightly. Gravity is not on your side if you try to swallow when lying down.