'I want to kill a dragon, but I need to do it on a budget'

Silver Sword is actually a bad idea against Moder seeing as she is completely immune to spirit damage. That means 1/3 of the swords damage is completely ignored. Modder is also immune to Frost, meaning Frostner is even a worse idea as it does spirit and frost, meaning less than 1/3 of the damage has any effect on Moder.

Draugr Fang Bow is the way to go, fully upgraded as you can. Obsidian Arrows if you have plenty, otherwise Poison Arrows. Moder is weak to fire but Fire Arrows do very little damage in comparison. Bring lots and lots of arrows.
The main key is to now waste shots. Don't fire unless you are certain you can connect, otherwise you'll run down your bows durability. If you don't waste many shot the fully upgraded bow will last you the entire fight. I still had over 1/4 left using poison arrows.

Other than that normal weapons, Like a fuly upgraded Iron Mace, but Moder is a very difficulty melee fight and can do attacks over 200 damage that are extremely hard to avoid in Melee range.

If you can pick a battlefield that gives you something to put between you and Moder when she lands. Either rocks or a pit. I had just mined out a silver node and the left over pit kept Moder from coming right at me, so I stayed on the opposite side and fired away whenever she landed, circling as she did.
Also set up a perimeter with torches or other anti-spawn items so you are less likely to get adds. Dealing with Moder plus a Golem is not fun.