Submit with only 2 LORs?

[BuildingMyOwnLuck]

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So my non-science LOR writer who said would finish her letter by last month, is on vacation until end of august. This one is kind of important as she was my PI (well I worked under a Ph.D student, so not directly under her) but I'm sure the student wrote me a great letter draft for the PI, so it would be a strong letter.
I already waited 2 weeks after I got my secondaries for this letter, and I don't want to delay any further.

1. Can I send out to the schools where they only need 2 letters? Or will only 2 look weird?
2. If so, when (if) I get my LOR, should I resend to the schools I already submitted to? I heard that can send me back to the queue.

Any advice is appreciated, thank you.

 

[BuildingMyOwnLuck]

1) send your secondary in now (I do not understand why applicants think they need to have letters before submitting

I didn't submit is because I believe I can't edit the essay responses after I submit, and while the delay is annoying, it's giving me time to constantly tweak and improve the essays, since the app won't be reviewed until it's complete anyway.
To be honest, I'm not 100% sure it would be strong, I'm just guessing, but to double check, there are no negatives submitting with only 2 I hope (to ones that only need 2 of course)?