Final answer:
The grammatically correct change for the sentence would be to change "didn't" to "don't" The correct answer is option c.
Step-by-step explanation:
To make the sentence grammatically correct, you should choose option c: Change "didn't" to "don't." The correct sentence reads: "She and I want to go to Europe by ourselves, but we don't have the money."
The sentence needs to be in the present tense to agree with the first part of the sentence, which uses "want," also in present tense.