I've read everyone's comment or response to you. Allow me to clarify - from my experiences and insight/knowledge being a "traditional Hmong" - practically ALL my life, and presently and likely to my last breathe on Earth.
Basically what everyone said is not "exactly correct", especially pajnpis -- about the food offering outside/backyard and paper money burning at night.
This is the typical/normal traditional Hmong belief and course of action.
1. First "why"? The reason your grandma came to you or your family in your dream(s), is in all likelihood (according to Hmong belief/rationale), is that those closer to her, meaning her sons/daughters - and this is where MovKuam was coming from - probably paid her no attention. They did not want to help her or do not care etc.. (Maybe they are Hmong-Christians or simply ignorante/ignoring your grandma.) You and your family are probably still traditional thus she intentionally came to seek help from you. Even if you or your family is not traditional, there is reason why she came to you guys. Maybe you guys love, care, and will help her etc..
2. The simplest and easiest way to help is simply to go and buy some "paper money" and burn it as offerings to her. It does not matter where, when, or how simply or fancy you want to make it. All you have to do is simply say, "Grandma, I am offering money to give you. Come and take it so that you may have and use it to your needs." That's it. You can even say it in English. Saying your grandma's name is not a bad idea either, as it is direct ...
You can do the same thing with food. And that does not mean you have to cook something specifically for her. (Examp: You can be having a Big Mac at the park or in your car. Just break off a small piece, add some fries, and a cup of water/pop and say, "Grandma, come and eat. I have food here to offer you. Come and eat." Yeah, that easy. Just throw the "offered food" away afterwards. You can even ask for blessings during both or all of these times, when you offer "money" and "food" to her.) NO! You or your family will not get sick or anything by doing any of these.
3. Lastly, the only time a "shaman" consultation is needed or is required is if after having dreams like these and you choose to do nothing, people within your family, randomly and unknowingly fall ill. Visiting the hospital or doctors has no diagnosis or cure. However, this case/instance is VERY VERY RARE, unheard of, especially if you/your family did what is in #2 (above) ...
Lastly, not required, but if your grandma's burial is close by and within driving distance, periodically you may want to go visit and bring some food/money to offer her. Just be sure to inform her to come and eat/receive her money. We do that for my grandparents at least once or twice a year or whenever we go and visit their burial -- offering flowers, food, and sometimes "money", but mostly flowers and food/water.