Given a context in which the houses are in fact numbered in a small community, then yes, it is possible to refer to it as "house # 7". But the context has to be mentioned beforehand because, as far as I know, houses in the US are not numbered. So they are not referred to using a number. Instead, the specific address or some other characteristic is used to identify it. I imagine this is similar in other English speaking regions.
The usage of "house #7" is similar to the usage with apartments, hotel rooms, etc. For example,
- John is in room number 105.
However, this is often shortened to
- John is in room 105.
Similarly, I think
- the lady who lives in house 7
is okay. I prefer in over at because at is used for specific street addresses in my mind:
- The lady who lives at 123 Fake Street ...
But I imagine that at is okay in 3 too.
Is there a more concise way? Yes, I think using from can suggest the same meaning.
The lady from house 7...
From is often used to indicate someone's origin, domain, home/hometown, etc.
from preposition (ORIGIN)
used to show the origin of something or someone:
I heard music coming from my room.
Someone from the bank just called.
Where are you from?
US Route 1 runs from Maine to Florida.