I developed a friendship with someone that started out as a physical therapist. Lately she has become extremely clingy and needy. She is constantly texting and if I don't respond quickly she immediately jumps on me, asking if something is wrong.
To me, she comes across as depressed but she flat-out denies this. I am not quite sure how to politely say that I am not comfortable with the overwhelming amount of contact she seems to need. I am disabled and have a house, husband, family, and other friends to fill my life. It's just too much.
It sounds like your friend may have a problem with boundaries---both in mixing her professional and personal relationships, and in being too clingy and needy with friends.
In a situation like this, you need to explicitly let her know when she has overstepped your boundaries. It is perfectly appropriate to remind her that you have responsibilities to others and to yourself. Clarify how much contact and what type of contact feels comfortable for you to have with her. For example, you can tell her that you value your friendship but can only speak by phone no more than x times a week or see her no more than x times a month.
It's always uncomfortable to set boundaries like this but it will be far more comfortable than letting her continue to encroach on your life.
Hope this helps.
Some prior posts on The Friendship Blog that discuss boundary problems: