Should I persevere with DD's swimming lessons?

Maybe take her yourself? They will learn to swim but in a less formal setting that won't cost you the earth. Swimming lessons are quite boring but going to the pool for a splash around with mum is more fun. You know her best so can find things that motivate her best.
Between me and my dh we taught our dc to swim. Once they could swim my dd wanted to go to swimming lessons to learn how to do it right🤷‍♀️

My daughter was like this at 4.she loved lessons for the first few weeks then hated it. I decided to stop lessons but just rake her myself now and then for fun. She resumed lessons when she was about 7 or 8 and is now a brilliant swimmer at 11. She's way better than me. If she's finding it stressful at 4 I'd leave it for a couple of years.

Also take her swimming yourself. Swimming lessons are like music lessons, you need to practise what you have been taught.

I’d stick with it now you’ve started.

personally i think there’s more benefit in taking them yourself until 5, but only if you can go every week, and only if you are very confident in the water yourself. until 5 or so it’s all about confidence, learning to float without bouyancy aids, jumping in, going under water etc.

One of mine was not progressing at swimming lessons at age 4. Two terms and little progress, becoming reluctant to go.
I took her out and gave it a rest for 6 months then enrolled somewhere else and she never looked back

I'd persevere. I agree with @happysm1, progress comes in fits and starts. She'll need to be able to swim to enjoy all the pool parties at primary school, and obviously important from a safety aspect too. She won't get more confident unless she's in the pool regularly.
Are the lessons very expensive? We pay £7.50 an hour in a class of 6. South east.

I took my now 5 year old out of lessons earlier in the year as he wasn't engaging and was getting scared of lessons. I take him swimming twice a week and when he's feeling more confident we'll put him back in. His sister did lessons from age 3 and is going strong 4 years later but they're all different.

pulling her out wont achieve anything positive. You may find like any skill: eg. reading, writing, they struggle and struggle and then just get it.
I personally think swimming is super important- my 4 year old spent the first 3 lessons of her swimming classes holding onto the instructor and screaming down the leisure centre. She's now progressed to stage 2.

Taking them swimming yourself and mucking around: splashing, etc. may help.

In my experience, and having sent two DDs through swimming lessons from age 3 onwards it takes a long time to see benefit. So my two had swimming lessons from a 3 yrs old and finished lessons in yr 6 so 10/11 and they are strong competent swimmers now. But it took time and there's absolutely no way you will see improvement after 8 weeks. You have to invest the time for your kids to be swimming well and it will feel like they are achieving nothing at times.

I'd persevere with teaching her to swim but teach her yourself.
She may not feel comfortable or may feel unsafe in a group.
Who better to put your trust in than your DM ❤️
I taught my DC to swim and I can't actually swim myself, stood in the shallow end, taught her how to float then armed DC with a float and arm bands, me shouting "kick your feet" whilst holding her up 😂
Great fun!
She swims like a fish now.
My greatest regret is not learning to swim myself

She's your DD so you know her best. Progress comes in fits and starts IME and I would keep going. My DD had a period of no progress, but realistically unless you can be bothered taking her yourself every week, she won't get the chance to get comfortable in the water. There is plenty to learn without getting your face wet. One of DD's friends (8) - she has sensory issues -still won't put her face in, but has mastered the arms and legs for breaststroke and front crawl, just not the breathing. It will come eventually.