AIBU to think work is BU about annual leave

[FirTree31]

Single parent to two primary school (just) boys. Our team has taken on extra work as someone has been asked to leave and they have not hired any one to replace him. One of my colleagues is also a parent (soon to be single) and I have in the last two days been declined two sets of annual leave, one for October and one for Easter holidays 2020 as she has already requested them. That means that when either one fo us books AL around school term we will be pitted against each other.
AIBU to think this is unfair and unsustainable. We are both master's students in our first entry level role, my issue is obviously not with my colleague, but with my line manager for pitting us lien this.

This thread (not the OP, just the topic) reminds me of a colleague I had in my old workplace who’d get really cross if childless colleagues got any time off at Xmas beyond the public holidays, as “it’s supposed to be for children”. In her view childless workers had a duty to allow parents to be off with their kids. Thankfully I don’t work there anymore but I often wonder if she’s changed her tune now her kids are older...

First come first served . So she's more organised than you . But surely she doesn't have enough annual leave to have all school holidays off ?
I've had this I've always booked in advance and people wanting to book short notice but sorry user has already booked it off it's fair play . You can't expect to be annoyed.