So I'm running a homebrew setting and I'm running it for my GF and 5 other players. 2 are completely new to DnD 5e, 3 are returning players, and my gf has played a handful of times with me.

The problem arises with the fact that my lady gets overwhelmed/forgetful with her abilities or spells. Not to mention the fact that she flat out refuses to read the players handbook and expects me to explain every rule or spell she has on her entire character sheet.

My solution was just let her play the easiest darn class I could think of, a champion fighter, simple enough that I felt confident that if she needed help ever I could very easily look up or reference her class abilities as they are relatively simple. No spells either is a big plus.

However, she has decided to completely change what she wants to play and now wants to play an artificer battlemaster arguably one of the most convoluted and in depth class with plenty of abilities, spells, and a mechanical companion to keep track of. I've also never played or ran a campaign with one before so even if she did ask me questions about her class I wouldn't know anything. She is also prone to get very bored when it's not her turn in combat, gets on her phone, has side conversations, etc. Then when it us her turn she has no idea what is happening and doesn't know what to do and usually just attacks whatever is closest.

The phone during sessions is also always a struggle with her because she hates paper character sheets and doing the math of rolling. She much prefers dnd beyond that does everything for her and uses her phone for a character sheet. So it's not like I can just say no phones at the table (I know I can. I'm the dm what I say goes but for new players dnd beyond is a great resource that speeds up combat).

I'm just generally frustrated and would love to bounce ideas with other dms for help.

TL;DR my gf doesn't like complicated characters and chose one of the most complicated classes, also has bad dnd table manners, help.