NOPE. A working band is not an exercise in socialism, it's a business and should be managed as such.
...
I bring thousands of dollars worth of gear to the gig, and play instruments that I have spent months customizing.
do those customized instruments add to the number of people who show up when you play?
There's a point where the low dollar value (and arguably the quality) of a musician's gear can affect the sound to such a degree that people stop coming to hear him/her. There's a point of diminishing returns where the high dollar value won't make a musician sound so much better that more people come to hear him/her. If the thousands of dollars worth of gear and the customized instruments you bring to a gig are necessary for your band to keep that gig and get others, then you have a point here. OTOH, if any of that "thousands" is because you simply wanted MIA instead of MIJ/M/K/I or because you wanted one brand over another, less expensive but just as reliable one, then the singer isn't responsible for that financial outlay.
If --example-- that Custom Shop '55 P-Bass or US '75RI doesn't bring the band any more money than a Sting or Geddy, then the difference ought to be your responsibily and not the band's. If, OTOH, you're losing gigs or not getting them because the bar owners won't hire a band whose bassist plays an SX or a Squier, you may need to spend more money and can justify that extra expense. It's a business and should be managed as such.
I understand fully that by "thousands of dollars" you may be referring to $2000 or $20,000, so only you can answer this for yourself.
I practice for hours so I can confidently play every song in the set and justify my cut of the pay.
If she's not getting done the job she's been asked to do, she doesn't need to be there at all. If she is, this is a moot point.
On top of that, I help lug EVERYONE'S equipment in and out of the venue (not just my heavy-a** stuff) and set up sound and lighting as well. We all pitch in.
If all someone did was waltz in and plug in a microphone, why they would have some "larnin" meted out by the other guys.
1) She's a woman, not a roadie. Are you asking her to help plug things in, turn things this way or that, put stands in place, etc., or are you saying that she ought to help lug in a bunch of 2x15s or 8x10s? I don't know how big or strong this vocalist is, but unless she volunteers, she doesn't have to do the big stuff in any band I'm a part of. You shouldn't even be asking that of her.
2) She's a vocalist. How many singers can --or need to-- match a musician for gear weight/bulk/expense?
When your backup singer expends the same amount as the rest of the band in equipment
See #2 above
and effort, and takes a more invested role, then she gets full band-member pay.
Right now, she is earning back-up vocalist pay; and IMHO you are paying her too much already.
Should have been dealt with up front.
If she's on stage with you guys at every gig, and is at every rehearsal... I think she probably deserves an equal cut.
Should have sorted this out when she joined.
Because it wasn't dealt with up front, I'd say pay the woman and forget about the difference in you own take-home pay.
Equal cut. You're quibbling over a few bucks. OTOH you could ask her to step up to the plate and handle lead vocals on a larger fraction of the tunes.
I've never expected to get paid for the gear that I own. It's my job to manage my gear investments so that I don't lose my shirt.
This.