Question: How to meet cousin without coming out over the phone?

My cousin is back from overseas. Since she is a lesbian with a 11 year old daughter I thought she could probably give me a lot of advice. Especially on how to come out to the family and how they reacted at the time. I know she came out when I was still in high school, but being at boarding school and a self involved teenager I wasn't really paying that much attention. 

Having a complete belief that stealing my brother's playboys was completely normal for a heterosexual girl probably didn't help towards me focusing too closely on her coming out either!

My problem? I don't see her that often, and when I do organise to catch up it always ends up as a luncheon including my sister, her daughter, my mum, aunt, my cousin's partner and her daughter!

I need to talk to my cousin without anyone else around, but I have no idea how to ask this of her without going into the reason on the phone. I mean what on earth is she supposed to think if I say I need to talk to only her about something. It's not like we've connected on other particular topics in the past.

She is a teacher, so I guess I could go in on that angle, but her partner is a teacher also, and I don't know her well enough to go into it with her too.

It will be especially obvious when I ask her not to mention us meeting to anyone in the family. I mean if I was going to meet her for advice about school years for my kids - I wouldn't be keeping that a secret from my mum.

I just don't want to come out over the phone. It would start a whole conversation that I'd rather have face to face.

I'd really like to talk to her soon, so any advice would be wonderful!!!