[escape_thereal_world]

Firstly, it is possible but unlikely.

Since she had food poisoning, that accounts for the nausea. Dehydration from hot weather accounts for the headaches. She has had normal length periods, which normally women who do bleed during pregnancy have very light or short periods.

So you have nothing to go on other than her belly is a bit bigger. Has she gained weight? Could she be bloating (caused by some foods, allergic reactions, water retention, etc.).

A typical pregnancy at 4 months would start to show (some women do not show until 8 or 9 months) - this depends on the person's body. First child of my sister's she was showing by 3 months. This time she is almost 5 months and has hardly any stomach.

Some women can go through pregnancy without any symptoms, though it isn't very likely. And other women get nausea, headaches, constipation, etc.

I don't think you have anything to worry about. She is getting regular periods. Has no symptoms. And isn't worried about it herself.