I'm afraid it will all just depend on the bank policy, if they have a policy in place not to lend for such buildings then income/site value etc won't matter to them. A lot of bank policy is very inflexible as there are no decision makers at branch level and hard enough to find anyone in the Head Office either who will go outside guidelines.
A broker might not be a bad bet, at least they will know which bank might be more inclined to lend for this purpose.
If the mortgage doesn't work out and she has a credit union account it might be worth asking them, she could get secured loan rate, it would be higher than mortgage rate and probably max 10/15 yr term but might be a solution if no other is available.