Not an ideal response from your mother but I wonder if your sister is an older sister, who has relationship questions that do need deeper investigation, whilst your questions are of a sort where your mother already knows the best answer without needing to investigate details, and feels that after giving advice she wants to get on ?
But whatever the cause, pick a good time when your mother isn't concentrating on something important to her, and calmly, politely ask why she doesn't give as much attention to your concerns as she does to your sister; as it makes you feel less valued. Do not allow unchecked emotion to turn a talk into an argument. It helps no one when two parties feel they are being attacked and need to defend theirselves.