Overbearing friend

I have a really good friend whom I am close with and I have no problem sharing secrets and being comfortable with, but when I’m around my family she acts different and it annoys me so so much. Around my mum especially, she buts into personal conversations that I’m having just because she was eavesdropping and completely takes the conversation away from me and my mother toward her and my mother. It is almost always about personal, family and relatives business to which she knows nothing about, knows nobody that we’re speaking about, or knows any backstory to what I was discussing with my mum, but she jumps in anyway. She gives her opinion (loudly) , disagrees with myself and my mother even though we’re the ones who know what we’re talking about, and tells us what to do with a situation she has absolutely no business in or knowledge of. I’m aware she has OCD and depression, she is also quite a confident and lively character, but she knows nothing of boundaries, what is her business, the rudeness of jumping into other people’s conversations or when to stop digging into the story. This absolutely enrages me, like I get so annoyed at her once she does this and I try to get her out of the conversation and bring it back to my mother and I, but she’ll always come back in even though we’re not talking to her. I’ve never said anything to her because ‘technically’ she’s just an interested friend, a chatter box and we are family friends so she isn’t a complete stranger to us, but this really affects me. I don’t know why but I feel like she’s trying to steal my mothers attention from me because I held the conversation initially and she wants in, and wants to be the one discussing with my mother. She has a very close relationship with her own mother (far closer than I am to my own mother even) and they are extremely affectionate and close, yet when it comes to my family members, she MUST get involved, either through questions, jokes or by forcing her way in to an ongoing conversation. How do I deal with this? Why does she do this? and doesn’t she notice at all how annoyed I get when she does this or how I try to block her from the conversation when I sense she’s taking over? At some point I stopped bringing her to hang at my house because I know exactly what’s going to happen and I will be mad and it will ruin my mood. Nobody hates her, she has no need to try this hard. I try not to push her away but I can’t keep this friend close to me forever if this is the behaviour I have to be around.