All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
First of all, we thank you for your keenness on being kind and dutiful to your parents and for your desire to help them. Being kind and dutiful to the parents is one of the greatest acts of worship that please Allaah, the Most Merciful. Please refer to fataawa 82254 and 87019.
The method of keeping ties varies depending on the circumstances; sometimes keeping ties can only be achieved by visiting the person, in which case it is an obligation to visit him, otherwise the person would be severing ties with him unless he had a sound excuse.
Al-‘Adawi, from the Maaliki School of jurisprudence, said, “Keeping the ties is achieved by visiting, giving money to the needy, and saying good words and asking about the situation and condition of the person ... Keeping the ties by visiting is for the one whose blood relations are near, otherwise one can keep the ties with them by writing to them or sending someone to ask about them.”
Therefore, if you cannot visit them, then you can keep the ties with them with whatever means possible. If your mother is safe from harm, then you are not obliged to travel to her, but whenever it becomes possible to visit her, then you should do so.
As regards worrying about your mother's illness, then this is natural as a person is predisposed to love his mother and hate that harm would afflict her.
As regards whether or not this could be a warning from Allaah to help her, then this is a matter of the Unseen which only Allaah knows, but the texts of the sharee'ah urge people to be kind and dutiful to their parents, especially when they are in need of help.
Allaah knows best.