Jelly Have you told her to ask the gardener, or ask the carer? Sometimes it needs spelling out. You think that a grown adult would be able to solve the problem by asking someone else, but I find sometimes I have to actually tell my Dad who to ask about something.
Do you see her regularly? If it's not life-threatening, be firm, say, "It'll have to wait till I see you on Thursday. Meanwhile - can you leave the bathroom door open and have the light from the landing?" ... for example. (Maybe not the best example ... you don't want her putting a table lamp in there on an extension lead.) Give the message that she can ask you to do jobs, but it may mean she waits a week or even a month, and it would be actually much quicker if she were just to ask the people around her.
Is she ringing your landline or your mobile? If the landline, can you just let her go to answerphone? If it sounds life threatening, you can interrupt her message and pick up, otherwise you phone back at your convenience. And switch the bell off if you're going to have some relaxing time - you can't relax if you're listening to a phone ringing and wondering whether to answer it.
It's difficult to do, but you have to cut yourself off emotionally, treat her as a problem to be solved, not as a person. Get away from the inner voices saying "but she's my mother" "but she's got Parkinsons".
Don't be to quick to condemn - consider the possibility that she actually does want your attention, but doesn't want to ask for it, and so is seizing on minor jobs as a "legitimate" reason to call you or ask you to visit. It feels like she only wants you as an odd-job person, but it may be the exact opposite - she's using you as an odd job person to get some time with her daughter. Or, of course, she may simply want you as an odd job person!