Couple on UC split up. what happens?

We have a case where a UC claimant moved in with his girlfriend and her baby daughter. They were added to the UC claim and IS and CTC stopped. They received UC for a few months but now he has left. I know that the lobster pot says that once on UC then you tend to stay on UC but as the partner on a UC claim would that apply to her or will she go back onto IS/CTC?

We are in an area that UC is accepting new claims for single jobseekers only.

Regulation 9(6) of the UC (Claims and Payments Regulations 2013 reads

“(6) Where an award of universal credit to joint claimants is terminated because
they cease to be a couple an award may be made, without a claim, to either or each one
of them–
(a) as a single person; or
(b) if either of them has formed a new couple with a person who is already
entitled to universal credit, jointly with that person.”

If she doesn’t want to be on UC, as a lone parent there is a route back onto legacy benefits

http://www.rightsnet.org.uk/forums/viewthread/9073/

This only works in areas with gateway conditions, but as you are in Wales you should be fine.