L.L.
Maybe you're underestimating the in home day care. Toddlers don't need tons of stimulation. Maybe she's got too much stimulation right now, and that's why she isn't walking. They need peace, and time to focus on all the huge achievements of young toddlerhood. In the long run, the in home might be more comfortable to her, more homey, better for such a huge transition...and what other option do you have, if she's not walking?
If you tell the people you're only going to use them for a month until she can walk, they probably won't accept her...and by not telling them, you are being misleading, and that's not the way to go. So that really isn't an option, in my opinion, unless they're really willing to accept her for such a short time. Doesn't seem like a good idea, though...as soon as she gets used to it there, you put her in montesorri.
And not to knock montessori school, but I don't like it, as a total environment, for young children who are spending so much time away from their parents. It's way too chaotic in how they "teach" (or how they don't teach, but let kids "discover") and forces them to grow up a little too quickly. Although I agree with a few of their practices, I'm just not a fan.