Some Russian cultural advice please

We're visiting Moscow in a couple of weeks, for a few days. Good friend of my partner has offered us her apartment. She will be away at that time staying at the family country house. She has no partner herself and lives on her own with her 1-year old baby.

I suggested via my (Russian) partner we can give her maybe USD 100-200 for this, but she rejects this. So I need some Russian etiquette advice. Is it the norm to say no to any money, but it would actually (particularly given her circumstances) be very welcome. Or will she instead be dismayed if I leave it in the house for her, along with some gifts we will take.

She's being polite and understandably proud Leave her the money and/or insist on giving it to her. With a baby, she can use it or save it for a rainy day.

Given that hotels in Moscow are so expensive, USD200 is a bargain for what you are getting, even if it is a humble apartment.

(Hint: give her more if you can afford it.)

A week at, for example, Ibis, would cost you €350 but there is no Ibis-type hotel in Moscow, AFAIK, only really-crappy-dorms that make Youth Hostels look nice or super-expensive (USD300 per night) expense-account 5-stars.

Remember that almost anything is available in Moscow now for a price you and I would find reasonable, and so you don't necessarily have to haul stuff all the way from London save for things you know are only available there (like preserves from Harrod's, etc.)

P.S. Euros are becoming more popular/useful in Russia than U.S. Dollars, if that helps, as you do live in a region that has now has a tunnel-border with Euro-land. ;)

I second that.

Bring a few toys for her kid and maybe buy flowers and a card before you leave. Flowers have always been a popular appreciation gift for women in Russia.

Some Russian cultural advice please

Is it the norm to say no to any money, but it would actually (particularly given her circumstances) be very welcome.

Yes, when being asked, it is a norm to say no to money. Mostly because of pride and also along the lines of the traditional Russian hospitality which comes from the heart and not from the wallet.
However don't let it stop you. Leave some money behind, even if you are disappointed in the accomodations ( and I hope you are not ). Small gift for the kid is another good idea. You can buy toys/clothes all over Moscow.
A box of chocolates is always welcome. Sometimes I bring a couple of CDs if I know the receipient's taste. A bottle of perfume, up-scale cosmetics gift set. But definitely leave some money behind with a thank you note. Believe me, it will be appreciated.