Going to have to ask my sister for a pretty big loan until income tax comes and I'm super nervous…

Going to have to ask my sister for a pretty big loan until income tax comes and I'm super nervous about it. I absolutely HATE asking her because she's the type to bitch until it's paid back but we could really use her help. My father in law FINALLY said he'd cosign on a house for us but my hubby has a bunch of debt so the bank didn't approve him. If we can just borrow the money until income tax then we can get a house which is way better to invest in instead of wasting 1k a month on an apartment.