<think>Alright, let's tackle this problem step by step. So, Betty wants a wallet that costs $100. Hmm, okay. The problem says she only has half of the money she needs. Half of $100 is $50, right? So she has $50 saved up already.

Wait, let me confirm. The total cost is $100, and she has half of that. Yep, half of 100 is 50. Got it. So far, she has $50.

Next, her parents are giving her $15 for the wallet. Simple enough. So that's straight $15 from her parents. Then, her grandparents are giving twice as much as her parents. Twice as much as $15 would be $30, because 15 times 2 is 30. Adding that to the pile.

Let me write these down: Her own savings are $50, plus $15 from parents, plus $30 from grandparents. Adding those together: 50 + 15 is 65, and 65 + 30 is 95. So total money from all sources is $95.

But the wallet costs $100. So how much more does she need? Subtract the total she has from the cost. So 100 minus 95 equals $5. Therefore, Betty needs $5 more to buy the wallet.

Hold on, let me check that again. Maybe I miscalculated. Let's do the additions again. Her own money is half of 100, which is definitely 50. Parents give 15, so 50 +15 = 65. Grandparents give twice 15, which is 30, so 65 +30 = 95. Total is 95. 100 -95 is indeed 5. Okay, that checks out. I don't think I made a mistake here. So Betty needs $5 more. That should be the answer.
</think>

Betty needs \(\boxed{5}\) dollars more to buy the wallet.

**Step-by-Step Explanation:**

1. **Total Cost of Wallet:** \$100  
2. **Betty's Savings:** Half of \$100 = \$50  
3. **Parents' Contribution:** \$15  
4. **Grandparents' Contribution:** Twice parents' amount = 2 × \$15 = \$30  
5. **Total Money Collected:**  
   \$50 (Betty) + \$15 (Parents) + \$30 (Grandparents) = \$95  
6. **Remaining Amount Needed:**  
   \$100 (Total Cost) - \$95 (Collected) = \$5  

**Final Answer:** \(\boxed{5}\)