Thanks very much for the further information, it definitely helps.
Because she is still producing stool a complete intestinal blockage is much less likely and that's good news. The other good news is that she is active an alert and feeling herself.
Causes of vomiting can be a gastrointestinal foreign body, eating something (bugs or plant material) that she should not, a toxin or internal organ disease, inflammatory bowel disease or, less likely because of her age, a mass in her abdomen.
If she goes outdoors she may be eating something that you aren't aware of that is making her vomit. I'd try to keep her in until this problem is sorted out.
For now I'd try an acid reducer to see if we can settle her stomach. You can try either:
1) Pepcid-ac (famotidine) at one quarter of a 10mg tablet per 5 to 10 pounds of body weight every 12 hours.
2) Prilosec (omeprazole) at one quarter of a 10mg tablet per 5 to 10 pounds of body weight every 24 hours.
These will reduce stomach acid and should help if this is related to simple nausea and gastrointestinal irritation from eating something she should not have. These are very safe and can be used as needed.
You can also try a bland diet of 2/3 boiled, white, skinless chicken and 1/3 boiled white rice in small meals frequently for a few days. If things go well in a few days try to convert her back to her regular food by slowly adding a little more regular, less bland, at each meal. It should take 5 to 7 days to slowly convert her back.
If her vomiting continues even with these measures she needs to see her veterinarian. If she refuses to eat, has a tense, painful belly or runs a fever of more than 103F rectally then she needs to see a veterinarian promptly. I do recommend having her stool checked for gastrointestinal parasites by her veterinarian either way as she is going outside now.
Please let me know if you have any further questions.