It's hard to get a bead on this series. It's very cute and fluffy, but I'm not sure if we're supposed to take Youzi's belief that her mom is gay seriously, and thus it's about her encouraging her mother to get a girlfriend, or if "the joke" is supposed to just be that Youzi has misunderstood the whole thing. Her mom seems to indicate the latter; she's, at the very least, not in an actual secret relationship with a woman at that point, but whether that's because she really is straight or just to preserve the ambiguity is unclear.
I think she's not necessarily dating any ladies, but It seems pretty likely she's gay. She considers the prospect of remarrying or even dating a guy to be unthinkable, and Youzi's observations that her mom seems so much happier when she's flirting with girls probably isn't just wishful thinking.
Engaging wild speculation drive:
I think the gist of it is that she lives in a country and works in an industry where it is a business advantage to "play gay", but it's frowned upon to actually be gay. So she's doubly incentivized to pretend that her real inclinations are just part of an act, she doesn't think she can actually date anybody so she doesn't want to get her daughter's (or her own) hopes up.
This is probably reinforced on Ren's side, idol singers are even more controlled in the industry than actresses.
