I’m making a warlock main villain

I’m trying to make a warlock main villain for my first campaign. I used to the Archmage stat block from the 5e monster manual as a basic template, then swapped spells out for warlock spells.

But since warlocks get way fewer castings than a wizard would without their boons/pacts, I gave her Pact of the Tome for a few extra cantrips and a follower of the Great Old One.

My friend looked at it and said I can’t do this since she isn’t a PC but a villain, so she isnt allowed to have the boons or other things a warlock PC would have. I pointed out that without the boon and other minor tweeks I made she would cast 4 spells than be unable to fight afterward, since without the boon or perks warlocks get next to no actual spell slots.

I’m just wondering if giving her the boon, invocations and arcanums would actually ruin the balance?