Hello, my name is***** and I have over 20 years of experience as a veterinarian. I'm sorry to hear that your pup Maggie is limping and sore pads on one foot.
This may indeed be related to plant material such as a sand spur or grass awn getting stuck between the pads.
Or this may be related to moist dermatitis between the toes.
Moist dermatitis is caused by the skin getting wet, sometimes from swimming or bathing and not getting dried off properly but most of the time they come from a dog licking, chewing or scratching an itchy area and breaking the skin barrier due to an allergic reaction or irritant of some type, allowing bacteria that normally live on the skin to get in the skin and thrive.
It is essential to get her to stop licking that area to allow the skin to heal. This likely involves placing an elizabethan collar so she cannot reach her paw and treating the underlying allergy or irritant.
Allergens can be inhaled (like grass pollen, dust mites or molds) or related to an insect bite or sting and you can use a combination of antihistamines and high doses of omega-3 fatty acids to help with those (they also help with the symptoms of flea allergy). In combination fatty acids and antihistamines work synergistically, much better than either one alone.
You can try:
1)Benadryl (diphenhydramine only don't use the combination products with acetaminophen or decongestants as they can be toxic) at a dose of 1mg to 2mg per pound or one 25mg capsule per 15-25 pounds of body weight orally every 8 hours. Dogs take a much higher dose per pound of body weight compared to people so don't let the size of the dose she would need concern you.
OR 2)Claritin (loratidine) at 5mg per 25 pound dog once or twice daily.
OR 3)Hydroxyzine at 1mg per pound orally every 8 hours.
OR 4) Chlorpheniramine at 4mg to 8mg per dog once or twice daily.
OR 5) Zyrtec (Cetirizine hydrochloride) at 1/2 mg per pound of body weight orally every 24 hours. That would be one 10mg tablet per 20 pounds of body weight. Make sure it is NOT the formulation with a decongestant (such as Zyrtec-D) because dogs cannot tolerate decongestants.
Some dogs do better on one antihistamine rather than another. Give the one you pick a week trial and if it isn't working try another. Be aware antihistamines can cause sleepiness or hyperactivity in some dogs. These side effects do wear off with repeated use.
Omega-3 fatty acids are fish oil products. 3V by DVM or Derm Caps ES are good brand name products. Use the high end of the dosing schedule for your pup's weight, which means if he is between doses go with the higher one. I recommend a dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give her 20mg of EPA per pound of body weight per day. For example an 80 pound dog could take 1600mg of EPA per day.
Clip the hair in the area around her pads very short and remove any caught debris. You can use a solution mix of Betadine solution (povidine iodine solution) and warm water, made to look like weak tea to clean the affected areas twice daily. Make sure you get the solution, not the scrub. This is an antibacterial and will dry the area out to allow healing. No need to rinse this, let it dry on her skin. It does stain horribly though so you probably want to do this outside. Clipping the hair stops bacteria from wicking into the site and allows the skin to breathe and dry. If the area between her pads is very swollen you can also soak her foot in an epsom salt bath to reduce painful inflammation and swelling and then clean with the Betadine solution.
In cases where the infection gets deeper than the surface of the skin oral antibiotics may be needed to treat deeper infection. If she isn't significantly better in 3-4 days she should see her family veterinarian.
If her paw is raw you should protect it when she goes outside by putting a baby sock over it, and then a baggie over that securing the top to her leg with masking tape (which holds well enough, but is easily removed without pulling out fur when she comes back inside).
Please let me know if you have any further questions.