Does anyone know the chances of getting a mare to accept a 1 month old colt, if she already has a 2 month old filly?

OK, so there is one part of horses that I just don't know much about, the mouth.  And I need some help, I have a 9 week old Quarab filly, she seems to have an overbite, about a 1/4 inch, I know this is called a "parrot-mouth"  and I have seen pictures , but hers isn't that big, and I am not sure if this will cause her problems, or if she will grow out of it, and is there anything that can be done about it.  Any answers would be very much appreciated. 

                               Thanks

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