I've been there a few times, bear in mind though I was always with a group, and I am male.
It's generally safe there, even in the evenings. I'd keep my money close, and don't expose how much you are carrying in public. If she has a purse, carry it over the opposite shoulder, so it can't be grabbed. Don't offer to carry anything from anyone. There's red light districts, but you'd have to go out of your way to find yourself in the middle of it. I went there to go diving, so I don't really know if there's any picturesque tourist landmarks. If she goes shopping at a market, don't accept the price the vendors give you. They are inflated for suckers. That said, there's all sorts of fun things you can buy out there.
The Manila American Cemetery and Memorial is a must see. All LDS missionaries leaving the Philippines go on a tour there before going home.
Also, going to a Philippino market is quite an experience. They aren't hard to find if you go out and about. I get a kick out of all the hanging animal parts and fish.
It's mango season right now, so your friend is in luck! There will be ripe mangos all over the place for sale. :mouth waters: There are different *kinds* of bananas too, which is fun. Street-side vendors sell a certain kind of banana fried with sugar, and they are so yummy! If you are brave enough, street vendors sell balut (usually only after-dark): boiled, fertilized duck egg. Having a Filipino companion might help to get a good price for the things being sold.
It will be the hottest and driest time of year, since April and August are when the sun pass directly overhead. (August is not as hot because of the storms constantly breaking the heat.) It is a thrill to see your shadow puddled at your feet, a sight you never see in the States. The moon looks different too. We would walk carrying umbrellas to keep the sun off, and a handkerchief to cover our mouth and nose from the dust and pollution.
Riding a Jeepney is another thing to do just for the experience. Hang on for a crazy ride! Those drivers are fearless. They honk for pedestrians to get out of the way, because if they don't, they'll get run over!
I never went to the beach, because my mission was so small, it was actually land-locked! It was the only land-locked mission in the 13 or so missions in the Philippines. I'm sure there are some lovely ones. Likely there is tourist information available there.
I walked all over the place in all sorts of environments in the Philippines with just my female companion and never felt in danger. I was pick-pocketed once, and a rather exciting chase ensued as the police tracked down my stolen purse.
From what I've heard, it is the southern part of the Philippines that tends to be dangerous. There is a higher Muslim population there, and I there were stories of people being kidnapped for "looking American." American missionaries were generally not sent there, only other Filipinos.