'She's at another house' or 'She's at another's house.'

Hi teachers,
Is Olivia at home?
a) No, she isn’t. She’s at another house.
b) No, she isn’t. She’s at another’s house.

Thanks in advance.

I wouldn’t use either. They sound completely unnatural.

No, she isn’t, she’s out.
No, she isn’t, she’s at Marta’s house.
No, she isn’t, she’s at a (friend’s/relative’s) house.
No, she isn’t, she’s elsewhere.
No, she isn’t, she’s somewhere else.

Beeesneees,
“It is wrong to dump our garbage into another’s compound.”
Is this sentence right or wrong?
Could we not say “another’s house”?
Please explain.
Thanks.

It isn’t wrong but it sounds unnatural. A native English speaker would not use ‘another’ in that way.

Beeesneees,
“It is wrong to dump our garbage into another’s compound.”
Please make this sentence natural to the native’s ears.
Thanks.

It is wrong to dump our garbage into someone else’s compound.
It is wrong to dump our garbage into a neighbour’s compound.

In the UK:
It is wrong to dump our rubbish into someone else’s garden.
It is wrong to dump our rubbishinto a neighbour’s garden.

Hi Beeesneees,
Thanks a lot for your help and given options.

RtL