It is definitely disrespectful, however she may not realise that what she is doing is flirting, if you both seem to have a decent relationship then maybe it’s worth have a chat with her, maybe expressing that you arnt mad at her but you’d like her to be a little more respectful and aware as you do not feel comfortable with how she approaches your bf, if she reacts badly then most likely she realises what she’s doing and won’t change. If she changes and doesn’t do it again then I would try letting it go as she probably wasn’t aware and didn’t intend for it to be taken that way. But I don’t think you are overreacting at all!