Shula's never been satisfied with anything. She likes the idea of adventure but bottles out at the last minute whenever she's found herself straying out of familiar territory.
I can't now remember why she and Nigel didn't make a go of things, but it's always seemed to me that Shula was jealous of Elizabeth's later involvement with Nigel and her status as lady of the manor. I think she belatedly realised that she could have had that. She'd have loved playing Lady Bountiful over at Lower Loxley, but she'd never have made such a good job of running LL as a business concern as Elizabeth has.
She wasn't very happy with Mark, who was exceedingly dull, but dependable, just like Alistair. She was consumed by her desire to have a child - remember when she lost the plot with Elizabeth after her decision to have an abortion rather than go through with her pregnancy by Cameron Fraser, and hand over the baby to Shula and Mark so they could adopt?
She behaved shamefully all those years ago when she got involved with Richard Locke at the same time as Alistair, in spite of the fact that Richard was living with Usha, who was Shula's friend and had been Mark's business partner. She bottled out of leaving Ambridge with Richard because it would have meant moving to Manchester and she found it unthinkable to be so far from her family. It was very clear back then that she was settling for second best by marrying Alistair. Dreadfully unfair on him, although he did also behave very badly over the gambling which was actually not very plausible, but let's pass over that.
I don't think Jill will be impressed by Shula's behaviour at all. I will be furious if we don't hear her reaction on air! Peggy will probably have some choice words too. Rather hoping for some bitchy comments from Usha as well. Alan will struggle with this.