I've been asked quite a bit about why this mod requires a patch to work with any other mod that edits Lydia, such as appearance replacers and changes to stat. Here's a full explanation:

Every single object in Skyrim has something called a "record" that contains all the information pertaining to that object. In the case of NPCs, records include things like race, stats, voice type, inventory, spells, their appearance, and many other things. Only one mod can edit a given record at a time. Two mods that edit the same record need to be patched.

I mentioned "voice type" in the last paragraph - voice type limits an NPC to only saying lines by their voice actor. For example, both Jon Battle-Born and Balgruuf the Greater have a voice type called MaleNord, both Vignar Gray-Mane and Olfrid Battle-Born are MaleOldGrumpy, both Arcadia and Carlotta Valentina are FemaleEvenToned, and both Ysolda and Olfina Gray-Mane are FemaleYoungEager. Audio files are all stored in folders that share the name of the voice type of the NPC (or NPCs) saying them.

Voice lines in Skyrim are not directly attached to NPCs, they're all contained in quests, many of which are totally invisible to the player. The dialogue is assigned to NPCs by adding conditions to it, which make statements like, "If the potential speaker is [insert character], they can say this line", "if this quest is at this stage, NPCs can say this line", or the one that pertains the most to why IFDL has incompatibilities with so many other mods: "if an NPC has this voice type, they can say this line."

Lydia's default voice type is FemaleEvenToned, which means that she can say every single line in every quest that has the condition, "if an NPC has the FemaleEvenToned voice type, they can say this line" with little to no other conditions that would block NPCs from saying it, Lydia is able to say that line. Examples would be things like, "What do you need?" or "Good morning." from the quest DialogueGeneric.
This left me with 3 options:

• Don't change the voice type (thus not causing compatibility issues by changing Lydia's NPC record), but have Lydia go from speaking in LMG Wilson's voice to Colleen Delaney's voice at random during gameplay.
• Change ALL the lines shared between NPCs that use the FemaleEvenToned voice type by adding a condition that prevents Lydia from saying them, causing a ton of compatibility issues since I'd be editing a ton of records, but no issues with mods that only edit Lydia's record.
• Prevent Lydia from having two different voice actresses in game by changing one thing in her NPC record - her voice type - and make patches with other mods.