You really believe that magick will prevent a pregnancy?
I'll address this as well, if I may... personally, yes and no. Will magick completely prevent pregnancy? No, not even a little bit. While I believe that anything is possible with magick, nobody can get that kind of focus and intent into a spell. But magick of this type is not black and white, it's about swinging the odds... using our example here:
Average litter size of the domestic cat is between 3 and 6. Assume that 6 kittens a year is right for this cat (I think there are 2 iirc, but the math works the same either way). That's already on the low end, cats have 2 heats a year, but that's the numbers we're given...
OP seems strongly against surgery. I think it's a decision based in unreasonable fear, and also again urge the surgery or birth control options, however, assuming they don't change their mind, lifespan of the domestic cat is 12 years. Assume middle age, so 6 more years. Female cats don't go through menopause, but they do lose fertility as they age. Let's figure 6 kittens a year times 6 years is 36, then subtract 5 or so for loss of fertility the last couple of years. That's 31 more kittens.
If proper spellwork adjusts odds in our favor, we could look at something like an average of 1 or 2 less kittens a litter, and at least one less litter in this cats lifetime. So 5 years (subtracting 1 litter) times 4.5 kittens a litter (average between subtracting 1 and 2 each is 1.5) is 22.5 kittens, round up to 23. Subtract 3 for loss of fertility as they age...
The difference between doing your spellwork and not is 11 less kittens on the streets. Now, it's still 20 kittens too many, I agree, but it is a difference.
Bluntly (which is a thing you'll discover I am quite often), my numbers may be a bit off (the adjustment for magick that is, I googled the cat statistics), but that's a third less, or quite a decent amount. Of course, like everything else in magick, individual results may vary.
Now, I think most of us here would agree in magick making changes to the physical world, and assuming that belief, I don't think my numbers are that far off.
To the OP... my numbers are probably close to what you can expect with magick alone. I would totally count that a success. Herbal remedies may help tweak those numbers a little, but dosing is almost impossible, as you only really know if you get it wrong. Were it me, I'd add either the drugs from the vet or the surgery (probably the surgery, add that also helps prevent other health issues), but I shared so you'd have the information, just in case.
Starwitch, I see your point, but I'd rather have 20 cats born without homes than 31. Just saying
So with thy all; thou hast no right but to do thy will.
Do that, and no other shall say nay.
For pure will, unassuaged of purpose, delivered from the lust of result, is every way perfect.
~AL 1:42-44