Okay, got it. Hollowed-out middle, not a great company, not much above you. Yeah, that changes things. So here's a question - do you like bookkeeping? Because actuarial exams and CPAs and the like are definitely continuing ed stuff that helps the company out if you take it on. And they make you more valuable for the next place. And hey - if you step up and fill in while the bookkeeper is on maternity leave, that makes you a department head! W00t w00t! and if she comes back (maternity leave is a life-changer) you have an excuse to move on somewhere else. The raise issue isn't a good one to pursue - you aren't going to get more scratch without more responsibility and by taking on more responsibility you look more attractive to other employers. I'd get with the bookkeeper and say "I want to do your job while you're gone and if you come back, I want enough skills to do something else. What do you recommend?"
I would be open to learning bookkeeping. I'm not sure if I would love it though at my current company. I might not even like it in general as right now I have pretty much the same routine and I kinda would like to change my job for a change of pace. The current bookkeeper seems pretty miserable at working the job. She often complains about things being piled on. The problem seems to be that the owner and the CFO will ask favors at the last possible minutes or sometimes they will never respond to emails on approval for things to be done. The bookkeeper will sometimes send out an email on things that need to be paid out and sometimes they are ignored for a while. I'm surprised that she came back after the first pregnancy. I have told my company in the past that I'm willing to learn new programs and they said they will keep that in mind.