Have to really be confident in the relationship for it to be enjoyable if you actually do really like her. If you aren't sure about her but really like her, you'll get jealous.
My girl likes women too, and awhile back we started talking about involving other women (threesomes etc) but it never really got off the ground until we talked and laid out some ground rules...I didn't want her hooking with up with girls when I wasn't there, and she had some random rules like she didn't want me cumming in another girl while I was fucking her or getting a BJ.
Wasn't a huge deal for me at all and we both enjoy it now that we are confident in where we stand with it. Key is to make it on her terms...if you push too hard for it to happen, odds are it won't.