It honestly depends on the betta girly's attitude and disposition.
Some are just as, if not more agressive than the guys, where as some are stressed way too easily. You probably wouldn't want one with either of those personalities. However, for the most part, girls are chill when added to already established community tanks. Now, if they were to added first and then have other fish added to 'their territory,' that might be an issue.
So long as the introductions go well, you should be fine. :) Make sure there are hiding spots for the girl as well as any other fish. Watch for aggression towards the guppies (I doubt there will be much if any at all). Watch for agression from the other fish towards the girl.
oh, and qt your girl for at least a week, especially if she is coming from a petstore. Sometimes they can carry illnesses that don't show up right away. If it's easier for you, just use a large tubberware (maybe 1/2 a gallon) and float it in the larger tank, of course completely cleaning out the qt tubberware at least once a day. This way she'll get used to the other fish as she is qt'd.
Last edited by JKfish; 05-15-2012 at 04:52 PM.