Hi, Laurie and Mimi (what a wonderful name!). What she is doing is perfectly normal - it even has a name: beaking. She will outgrow it in time but if it really bothers you, simply push her beak away very gently and say "No beaking" or whatever other term you would like to use. The word itself doesn't really matter although I, personally, like to use the correct one so they learn it in a cognitive way.
But, also personally, I would not prevent her from doing it unless it hurts -and this is also very common because, when they are young, they still do not know their own beak strength (in this case, I say: "Be gentle" and, when the bird decreases the pressure it applies, I praise, praise, praise). See, this beaking is just their way of preening you, a sign of affection. Your clothes are your plumage and that's why she does it on you but not on the toys made out of material in her cage (they know they are not alive and they do not love the toys the way they love their human). Do you have children? If you do or are familiar with little ones, you know that when they are babies/toddlers and they are trying to caress or pat you, they would, instead, smack you - and sometimes, they do it hard
Well, it's the same thing with them with the added 'extenuating circumstance' that we are such inadequate 'birds' because, if we were real birds, this would not bother us at all. But, sometimes and under certain circumstances, one needs to eliminate a behavior that although it is normal, it's too painful for us. For example, I have had to teach some of my birds not to 'preen' my hands. I have an autoimmune condition that attacks my joints and my hands not only have age spots on them, they are a bit deformed and, because I have scrubbed so many cages, bathed so many dogs, washed so many floors, etc, my veins stick out much more than what is normal. They, apparently, think that these 'weird things' need to go so all the new ones are always trying to 'preen' the 'blemish' off my otherwise perfect plumage
So, whenever they go for them, I gently tell them: "No, don't touch" (which all my birds know and obey) and praise, praise, praise when they do. Parrots are extremely intelligent and so very eager to show us their love and make us happy that, in reality, it doesn't take very long to teach them not to do something if we are gentle, persistent and consistent about it.
Let us know how it goes but remember that this is a normal behavior (so it will take a bit long for her to stop), and that it actually means Mimi loves you.