Something similar to this happened to me on the sister site, WYP. About a week before I had a date in a nearby city to meet for lunch, I got an offer to meet another POT SB in the same city. Of course, I scheduled a dinner date and booked a room nearby. Also made reservations for lunch and dinner at separate restaurants.
On the way to pick up the lunch date, I texted her to confirm and tell her where we would be eating (Italian). She texted back and told me she was training for a fitness model show (I know, right?) and couldn't eat pasta - preferred fish. So I looked for another place, booked it and told her. She replied "Great! My sister is a bartender there."
Got to the restaurant, sat down for lunch, opened a bottle of rose and things went well... until she mentioned that her other sister (not the bartender) told her about the site and that her sis had a date later that night. My fork stopped moving half way to my mouth, and a very tasty bite of sea bass fell on the table. I fessed up that I had a second date and we compared names. Busted.
Turns out she is one of 11 sisters all living in that city, all between 19 and 45 years old, and 4 are single and using SA. We got a good laugh out of the situation. She appeared totally cool with it and we finished lunch. The rose did it's job and I mentioned that I had some "down time" before I met her sister and offered to show her my room. Negotiated a minimal $ p4p and made a solemn promise not to tell sis about our extra fun and off we went.
After dropping her off at her place, went back to the hotel, cleaned up and headed to the (same) restaurant to meet the second sister. The bartender sister served me, told me she was fully briefed by sis #1 (except for the hotel bit) and hooked me up with free martini's. Unfortunately, this did not end up as the Penthouse Letter you thought it was - sis #2 never showed up. Texted me apologizing saying she was "stuck" in Napa with her friends and would not be back soon. Promised to come to my city next week to make it up to me. She did; nice lunch but nothing more.
As it turns out, I dodged a bullet and got a bonus fuck out of it all.....
I found out 4 months later from another POT SB from the same city (not one of the sisters) the following:
She met a guy who had a terrible meet with a POT SB from that city about 4 months earlier. He agreed to take her wine tasting in Napa. She showed up for the date - with THREE KIDS and asked him to take them to Target for some things the kids needed. This poor schmuck agreed, spending about $400 on the brats and then took her to Napa, with the kids. That's why she was too late to meet me that night.
Naturally, I never accepted a meet with anyone from that city again.
So my advice, if the relationship is new, you might have an option to tell her you do have another meet as part of your process to choose just one for a LTA. Benefits: you could end up with a duo of SB's to play with, even a standard 3-way for BCD! Risks: She could bail on you and have her roomie bail as well.
If you are already fairly established in your SD/SB arrangement, bail (delay) on the roomie as described above