Toddler Sleep regression since new DD

[Slumberparty]

2 year old DD used to sleep really well. She got into the habit of going happily straight off to sleep after a story with no fuss. She would mostly sleep through but if she woke in the night I would just need to tuck her back in her cot and she would go straight back to sleep. 2 weeks ago I had DD2 and DD1's sleep has seriously regressed. She won't fall asleep on her own at night or for naps unless I stay in the room until she drops off and then sneak out. This can be hard to do as I am BF DD2, and DD1 only wants me to stay with her.
Last night was tough as she wouldn't settle and ended up in my bed. Between both DDs I was awake from 1-6am last night and am exhausted!
I am thinking about starting controlled crying with DD1 again - I did it when she was 1 year old and worked a treat. But I feel a bit mean doing it as I assume she is just insecure right now and wants reassurance that I am here for her?
Shall I sleep train or shall I put it on hold for a while and hope that she starts to settle herself again after a while?

Definitely hold off for a while. If she’s feeling out of sorts because of the new arrival it will make her feel much worse. Hopefully it will resolve itself when she starts to feel secure again.

I'm following as I'm in the same situation, although my dd2 is 6 months old. Dd1 currently in my bed and partner in dd1s room to make space.

Same situation, DCs are 1 and 3 years old and DC1's sleep has become a disaster since DC1 was born. I have tried everything and nothing has worked for more than a few days. Has not resolved itself. So I am watching this thread desperate for tips.