I am someone who deeply cares about social justice. The other members of my family care less about those things than I do. Now that I am aware of a lot of social issues, I can see things that I didn't see before. This means that, sometimes, when I hear my family talking, I can see that they are not as inclusive and as open-minded as I would want them to be.
Here is what I try to do in my day to day life to open the eyes of my family. It's a long process, and some member of my family are more responsive to it than others, but it's working (even though it's clearly not as fast as I wish it to be).
Lead by example
If you want your wife to be more open to bisexual people, you need to be open yourself but, most of all, you need to show that.
If someone is badmouthing bi people, you need to take a stand and publicly call them out. It's not an easy thing to do but it shows other people where you stand, it shows that you have strong beliefs about that and it might leads other to believe that you have good reason to be so sure of yourself.
If you do it again, and again, and again, at some point, they might join you into thinking that be people are nice, regular, human being.
Normalize the subject
Don't treat this subject as a taboo. Doing so implies that there is, indeed, something wrong about being bi. Instead, talk about it often and casually. For example, if someone assumes someone else sexual orientation, say something like this:
Or they might be gay. Or bi.
You don't need to make a big deal about it. Just treat the fact of being bi as a normal and unsurprising possibility and it might become a normal and unsurprising possibility for the other members of your family.
Share your knowledge
When I'm interested in a subject, I read about it a lot. When doing so, I often find articles who made me say "if only my family read this, I'm sure they would be more tolerant toward X". So, when I find an article like this, I share it with them. A warning though, don't do this too often. If you send them too many articles, they will just stop reading them.
If sharing articles is not a possibility for you, you can also share little facts that will help your wife see bi people in a positive light (or, at least, make her feel bad for them. Like if you talk about LGBT+ people suicide rate). I usually do that during the meal or while we are on the road. You just need to find a time where your wife is open to chitchat/talking.
Warning: If your wife isn't responding well to you sharing those things with her, don't push it too much. If you push too much, your wife might close herself to the subject and you will lose all chance to convince her that bi people don't need to be "fixed".
As a final note, I just want to say that you really need to be patient. I don't think you can get your wife to accept bisexuality before your daughter comes out (because that could take 10, 20, 50, 70 years or more) but I strongly believe that you could, at least, improve things. Even just a little, even if you don't see it.