PaulaBright, in that case you have to ... clarify (???) what the main reason for this reviews - 1. generate leads with possible sales her/his website to , 2. get website ranking which eventually will lead to better position in SERP , 3. to make the brand name more recognizable.
Keeping it in mind - evaluate the donors' sites (because depending on the reason, criteria for donor site will be different.
I suppose you don't need NN3. For NN2 you need donor sites with good page ranking and trust and some traffic, so people would follow the link from time to time and you need good amount of sites like that. For NN1 - sites with big traffic, even if PR and trust are not so good.
Another thing, to be honest, product reviews don't attract a lot of readers. There is another way of doing things - run competition. Which might have some review as well if they're ready to give 2 products to the same site.
Anyway, right down what you think, we might have some ideas suitable to your friend. At the moment I've got only those -
- think about competition (above)
- see what's on twitter on #pblogger #pbloggers look at the sites of those whose tweets you like and see if it's suitable donor sites
2a. consider websites of local parenting magazines, some of them like to publish reviews of promo articles as well. Article in printed version will be expensive but you ask internet only, it might be the same as with bloggers - would cost the product only
- contact mumsnet department for advertisers and see what's they have on offer, them might have something that your friend would like and with the amount of people visiting mumsnet it will be quite an exposure...