should I just focus on exclusively breastfeeding the now?
Yes!
Forget pumping - it's not representative of how much milk you are producing.
Put her to the breast as often as you can and especially at night between 1 & 3 am. This is the time when prolactin levels are highest so feeding then will really stimulate supply. (I'm not saying wake her up to do it, just that she'll probably need feeding around then, and make sure this is from the breast, rather than expressed or formula).
You are doing great - she will be your guide; if she's latching well, feeding & content, wet & dry nappies - all is good. All the same signs you had before.
However, I'm really sorry to hear your MH has suffered. Don't put b/f ahead of that - if you feel that b/f is adding to any issues, formula feeding is absolutely fine.
You are not letting your DD down - and you need to be well to care for her & your other DC.
Whatever happens is fine. Best of luck - & congratulations 👶🏻