Are you absolutely positive? Are you talking about urine or stools or both?
Is her stomach/abdomen distended and hard? Painful to touch?
How old is she? Is she spayed?
I understand how difficult this must be. I think we've all been exactly where you are at one point or another. I know that I have!
The thing I'm concerned about is that forcing her to eat/drink could just cause more harm if there's a blockage intestinally from eating something she shouldn't have. This would cause her to go off her food and water, plus stop going to the bathroom, but I'm pretty sure you'd have no doubt about her abdomen being enlarged, hard and bothering her when you touch it.
The next possibility is a parasite. She may be losing blood internally and while you might get her to eat and drink, you could just find her 'gone' at any time. Not what you want the kids to discover
Check her gums for color. If you notice they're pale, yellowish, white, grey or any combination of these - it's an emergency.
A cat can go for several days without a bowel movement, but this may contribute to hard, impacted feces that are difficult to pass and may need medical intervention to remove. When constipation is chronic, laxatives such as lactulose and cisapride may be prescribed.
If she's not urinating, it may be only a matter of hours before toxins build up and prove fatal. When a cat stops urinating or there's any pink/blood in the urine, it is a medical emergency. You don't have much time (this often means you must find an emergency clinic in the middle of the night, on holidays or weekends).
Home options that may be tried if the constipation hasn't lasted more than 24 to 48 hours is to withdraw kibble/hard food and offer a high quality soft food or home made dinners of boiled chicken (or lean hamburger) with rice and broth (never any bones). In instances like this, a fatty fish may also be offered; however, a regular or ongoing diet high in fish is not recommended for cats and may cause other health problems.
Offering a soft canned food with 1/2 teaspoon pumpkin (not pie mix, the real 100% pumpkin), a sprinkle of bran cereal or some Metamucil, Konsil, Siblin (a few drops in their food) may provide a quicker solution.
There is a controversy about offering a couple drops of mineral oil. Some professionals strongly advise against it because it may be inhaled and cause severe problems; others feel it's just fine on occasion for episodes like this. I feel it's a personal choice. I've never had to use it, finding huge success with soft food diets in our cat rescue efforts.
Here are some options for financial help, which you'll need to get her spayed if she's not already (unspayed females have a huge potential for really costly disease and health complications, and let's not forget the expense of kittens that no one wants):
If you have a Pet Smart in town, they often have the numbers for rescue organizations that may also help, at least with recommendations for where (or who ) to go.
I really hope this helps - and that everything works out for you and your family.