Have you and the gf connected much emotionally? Until recently I always felt rather inexperienced with women. I really wasn't, but because I'd never really had multiple, fulfilling encounters with the same women I didn't feel comfortable initiating or really being that forward about giving. As soon as I got comfortable with my now gf, that all changed. I WANTED to give, I WANTED to initiate, I WANTED to be intimate. I really think the change came when I started to really care about her. Granted, that is my personal history and I am quite sure it is different for everyone, but I really feel like she would be getting more comfortable sexually after a couple of months if she was comfortable with the relationship in general.
Also, what does it mean to be 'newly bisexual'? Does it mean she just realized she was bisexual or she just suddenly started being attracted to girls? Also, did you two meet her TOGETHER or did one of you meet her and then introduce her to your spouse? I guess my concern would be that she might not actually be bisexual but thinks the only way she can stay in this situation is by saying she is. I may be waaaayyyyy off there, though. You may want to back off sexually until you all figure out more definitively where you stand. It seems like everyone is feeling pressured by the sexual relationship (your husband by being the only one to satisfy you, you by having to see how compatible they are AND by not being fulfilled by your relations with her, and her by feeling pressure to be more giving with you). Maybe the emotional/intimate connection needs to be the center of attention for a while.