There are probably many different things going on here, but let’s focus on the ones you can control. Have you talked to her in private, giving specific examples of things that have bothered you, without coming across as angry or resentful? Have you thanked her for pointing out the things you have changed or implemented? If not, start there.
Consider also – is she acting out of fear or uncertainty about her future when she points out what you are doing “wrong”? Is she trying to convince you that you need her, and should therefore extend her contract? Does she feel responsible for making you a “success” since you purchased the practice from her, and is this her way of trying to ensure that?
Whatever her motivation, remember – you’re now the owner and your leadership should not be in question. Her actions are probably bothering others as well, and they need to see you taking charge. Be compassionate and understanding, but make your feelings known. Letting them fester will not to anyone any good.